Session initiation protocol (SIP) is a widely deployed application-layer control protocol for initiating, modifying, or terminating VoIP call sessions. The transmission of the voice and/or video stream itself uses another application-layer protocol, the real-time transport protocol (RTP). The RTP header contains information such as the synchronization source (SSRC) identifier which identifies the source of the stream. The SIP packet body contains, among other things, session description protocol (SDP) information such as the port numbers and codecs used for the RTP media stream. An SIP user agent is a network endpoint device that can create or receive SIP messages. An SIP user agent is typically identified by a globally unique uniform resource identifier (URI) of the form sip:username:password@host:port. SIP also has a globally unique Call-ID header value which identifies SIP messages belonging to the same dialog or registration. The Call-ID, however, is often changed as SIP packets traverse intermediate devices between endpoints, so it is not a globally constant identifier. Moreover, SIP does not use a globally unique and constant session identifier for a particular call, where a “call” is defined as a particular RTP media stream that flows during a session between two endpoint devices. As a result, it is often difficult to identify the endpoints and network path used for any given SIP call in a VoIP network.
For example, an RTP media stream that is transported between endpoints of a VoIP network typically passes through many different intermediate devices and IP networks. In order to troubleshoot network impairments that negatively affect call quality, network operators must manually identify all of the elements processing media as well as determine the path or “hops” through the network that the media is using. This can be a very time consuming process as network operators must manually match statistics from different network elements using a combination of call timestamps, phone numbers called and call duration.